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72
ABDOMINAL ULTRASOUND
rescan after the patient has resumed a normal
diet.
Biliary stasis is associated with an increased risk
of stone formation. 40
Biliary crystals
Occasionally, echogenic bile persists even with normal
gallbladder function (Fig. 3.45). The significance
of this is unclear. It has been suggested that
there is a spectrum of biliary disease in which gallbladder
dysmotility and subsequent saturation of
the bile lead to the formation of crystals in the bile
and also in the gallbladder wall, leading eventually
to stone formation. 41 Pain and biliary colic may be
present prior to stone formation and the presence
of echogenic bile seems to correlate with the
presence of biliary crystals. 42
Biliary crystals, or ‘microlithiasis’ (usually calcium
bilirubinate granules) have a strong association
with acute pancreatitis 43 and its presence in
patients who do not have gallstones is therefore
highly significant.
Obstructive causes of biliary stasis
Figure 3.45
Biliary crystals.
Pathological bile stasis in the gallbladder is due to
obstruction of the cystic duct (from a stone, for
example) and may be demonstrated in a normalsized
or dilated gallbladder. The bile becomes viscous
and hyperechoic. The biliary ducts remain
normal in calibre. Eventually the bile turns watery
and appears echo-free on ultrasound; this is known
as a mucocoele (see above) (Fig. 3.8).
Bile stasis within the ducts occurs either as a
result of prolonged and/or repetitive obstruction
or as a result of cholestatic disease such as primary
biliary cirrhosis (PBC) (Chapter 4) or PSC. This can
lead to cholangitis.
Haemobilia
Blood in the gallbladder can be the result of gastrointestinal
bleeding or other damage to the gallbladder
or bile duct wall, for example iatrogenic
trauma from an endoscopic procedure.
The appearances depend upon the stage of evolution
of the bleeding. Fresh blood appears as fine,
low-level echoes. Blood clots appear as solid, nonshadowing
structures and there may be hyperechoic,
linear strands. 44
The history of trauma will allow the sonographer
to differentiate from other causes of haemobilia
and echogenic bile, particularly those
associated with gallbladder inflammation, and
there may be other evidence of abdominal trauma
on ultrasound such as a haemoperitoneum.
Pneumobilia
Air in the biliary tree is usually iatrogenic and is frequently
seen following procedures such as ERCP,
sphincterotomy or biliary surgery. Although it does
not usually persist, the air can remain in the biliary
tree for months or even years and is not significant.
It is characterized by highly reflective linear
echoes (Fig. 3.46), which follow the course of the
biliary ducts. The air usually casts a shadow which
is different from that of stones, often having reverberative
artefacts and being much less well-defined
or clear. This shadowing obscures the lumen of the
duct and can make evaluation of the hepatic
parenchyma difficult.
Pneumobilia may also be present in emphysematous
cholecystitis, an uncommon complication
of cholecystitis in which gas-forming bacteria are
present in the gallbladder (see above), or in cases
where a necrotic gallbladder has formed a cholecystoenteric
fistula.